1. Technical Field
The present invention relates to linear error compensation of a touch panel, and more particularly to a linear compensation method of a touch panel that enables a touch control computer system to correct errors caused by the variation of the temperature itself.
2. Related Art
A touch control display has a touch panel combined with a display panel. The touch control panel allows a user to directly touch an icon or a menu displayed on the display panel so as to rapidly operate a computer system. In fact, the user touches the touch panel disposed on the display panel, and the touch panel feeds back a positioning signal to the computer system, such that the computer system converts the positioning signal to a coordinate value and then maps the coordinate value to an image displayed by the display panel.
The categories of touch panels include resistive touch panels, capacitive touch panels, electromagnetic touch panels, etc. A has advantages that structure is simpler and cost is low. Therefore, the resistive touch panels are widely applied in a variety of portable electronic devices. In generally, a resistive touch panel includes two transparent plates with a transparent spacer disposed there-between, such that a small gap is normally kept between the two transparent plates. Transparent conductive films, for example ITO films (Indium Tin Oxide films), are disposed on surfaces of the two transparent plates facing each other. When the transparent plates on the external sides are pressed and deformed, the transparent conductive films contact each other, such that an electronic circuit of the touch module detects a surface resistance which can be resolved into two resistances in two-dimensional directions. The surface resistance is introduced in a surface resistance-coordinate conversion procedure, so as to derive a position where the transparent conductive films contact each other, i.e., a position on the touch panel.
A transparent conductive film is generally fabricated by RF sputtering, and goes through printing, inking, baking, assembling, hot stamping, and other processes during the combination with the transparent plate. The aforementioned processes always damage the uniform distribution of the transparent conductive film, such that the actual surface resistance varies and cannot match with the actual touch position. When a coordinate point of the touch panel is touched, the actually generated surface resistance is different from the preset one, and a wrong coordinate is obtained by introducing the actually generated surface resistance in the surface resistance-coordinate conversion procedure. For example, when a touch pen is used to contact the touch panel, a linear error is generated between a point of the touch pen and a position of a cursor when the cursor is moved to be below the point of the touch pen.
In the prior art, a multi-point calibration procedure is further performed to correct the surface resistance-coordinate conversion procedure, so as to implement a linear error compensation for the coordinate. Under instructions of multi-point calibration procedure software, the user sequentially touches 5, 9, or 25 pre-determined reference points with known coordinates to obtain corresponding reference surface resistances. The surface resistance-coordinate conversion procedure converts a surface resistance output from the touch panel into a corresponding coordinate based on the coordinates of the pre-determined reference points and the corresponding surface resistances thereof through interpolation, extrapolation, or a specific algorithm.
For the resistive touch panel, environmental factors, especially temperature, seriously influence the actual surface resistance. For example, the user acquires a reference surface resistance of a pre-determined reference point at 20° C. for conversion by the surface resistance-coordinate conversion procedure. The reference surface resistance of the pre-determined reference point is only suitable to be introduced in the surface resistance-coordinate conversion procedure for calculating a coordinate corresponding to a surface resistance at 20° C. If the temperature sharply varies in a short time, for example, the user walks from inside a vehicle at 20° C. to the outside at −20° C., the actual surface resistance will vary greatly. As a result, the original reference surface resistance acquired at 20° C. is no longer applicable, and the user must perform the multi-point calibration procedure again to generate a new reference surface resistance. However, for ordinary users, it is difficult to determine at what temperature difference the re-calibration is needed, and the re-calibration from time to time also brings inconvenience to the use of a touch computer device.